Magnetic Nano-Ferrofluids: Study of Their Structural, Magnetic, Catalytic, and Toxicological Properties

There is a growing demand for biocompatible, non-toxic nanomaterials with specific functional properties, including catalytic activity. In this study, magnetic iron oxide nanoparticles were synthesized via chemical co-precipitation in the presence of polyethylene glycol (PEG). PEG was used as a coating agent to reduce particle agglomeration. Comprehensive characterization of the synthesized nanocomposites was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX) and vibrating sample magnetometry (VSM). SEM studies confirmed the nanosized structure of the particles with an average diameter of 20–60 nm. The saturation magnetization values were 57.37 emu·g−1 for nFe3O4-PEG6000, 11.95 emu·g−1 for nFe3O4-PEG4000 and 3.97 emu·g−1 for nCo0.5Ni0.5Fe2O4-PEG4000. In addition to their high magnetic properties, ferrofluids exhibited peroxidase-like activity, which makes them highly suitable for bioanalytical and biomedical use. The Michaelis–Menten constant (KM) for hydrogen peroxide ranged from 1.15 to 4.98 mM. Transmission electron microscopy (TEM) proved the penetration of the nano-ferrofluids into the yeast cells of Ogataea polymorpha. The studied nano-ferrofluids were found to be non-toxic at concentrations up to 0.2 mg·mL−1 for both prokaryotic and eukaryotic cells, showing no inhibitory effect on the growth of the bacterium Escherichia coli, the yeast Ogataea polymorpha, or animal and human cell lines. These results indicate that the advantages of synthetic nano-ferrofluids—including peroxidase-like activity, strong magnetic properties, cost-effective synthesis, stability, and low toxicity—make the synthesized nano-ferrofluids highly promising for future biomedical and bioanalytical applications.